Seals for semiconductor production apparatuses are used in processing chambers for etching the surfaces of silicon wafers, etc. as semiconductor substrates or forming thin film thereon, and thus must have a high heat resistance, a low gas permeability, low dust generation (less generation of dusts from seals), etc.
Plasma irradiation is carried out in the oxygen or CF4 atmosphere during the silicon wafer etching treating, etc., and thus gases such as oxygen, halogen, or the like are brought into the excited state, so the seals for semiconductor production apparatuses are liable to deteriorate, or their surfaces become brittle, and the deteriorated, and brittled materials are scattered away to deposit on the silicon wafers. These involve serious inconveniences. Thus, the seal material for the semiconductor production apparatuses must have a plasma resistance in addition to the afore-mentioned properties, e.g. heat resistance, etc.
To meet the requirement for use at elevated temperatures such as 300° C. in the semiconductor production apparatuses, cyano group-containing perfluoroelastomers, etc. having a high heat resistance have been proposed for use. To satisfy the required plasma resistance, on the other hand, a cross-linkable fluorine-based elastomer composition, which comprises a cross-linkable fluorine-based elastomer component and fine aluminum oxide particles having an average particle size of not more than 0.5 μm, or a perfluoroelastomer composition, which comprises a reinforcing metal-containing filler and titanium dioxide substantially without any elemental carbon has been so far proposed.    Patent Document 1: WO 01/32782    Patent Document 2: JP-A-2000-502122    Patent Document 3: U.S. Pat. No. 5,696,189
Such fillers as silica, barium sulfate, alumina, aluminum silicate, etc. are effective, when added, for preventing weight reduction in the plasma-irradiated atmosphere, and ultra-size reduction of particles to less than the interlinear space distances of fine patterns formed on the semiconductor, can attain effective filling of the ultrafine particles state into the interlinear spaces of fine patterns, thereby preventing unwanted short-circuit.
In some cases, however, such elements as titanium, barium, and aluminum themselves must be forbidden to use in the semiconductor industry, and now silica is only an available material. So, a composition, which comprises 100 parts by weight of a fluorine-based elastomer, 1-50 parts by weight of silica, not more than 1 part by weight of a metal element, not more than 1 part by weight of carbon black, and 1-10 parts by weight of an organic peroxide, has been proposed.    Patent Document 4: JP2,858,198
There is a correlation between the silica particle size and the weight reduction by plasma. The smaller the particle size, the better. The afore-mentioned cyano group-containing perfluoroelastomer, when used, has a poor compatibility with a vulcanizing agent, and so involves such a inconvenience as development of deposits on the surface of product after vulcanization. That is, the cyano group-containing perfluoroelatsomer, when used as a fluorine-based elastomer in the prior art of the afore-mentioned Patent Document 4, involves a difficulty in satisfying the balance between the weight reduction by plasma and the compatibility with vulcanization agent.
Silica includes wet process silica and dry process silica. The wet process silica contains moisture that can show some influences on the vulcanization rate or product foaming, and further contains more impurities such as Na2O, etc. than those of the dry process silica, so it is preferable to use the dry process silica in the vulcanization, rather than the wet process silica. However, the dry process silica has a large thickening effect, resulting appearance of melt fractures on the surfaces of extrudates, with increasing hardness of the extrudates. Thus, the silica content is limited. The smaller the silica content, the less the plasma resistance. Furthermore, the single dry process silica-based products are semi-transparent, resulting in development of spotted patterns (flow marks as composition flow patterns). That is, there is such a problem as loss of uniformity in the product appearance.